There is a desire to use gaseous fuel in marine vessels due to its combustion being cleaner than that of heavy fuel oil or marine diesel oil, and also since nowadays it can be more available than said traditional fuel types. It is known to use in LNG (liquid natural gas) cargo ships, fuel from the cargo tanks for the ship's propulsion, e.g. from U.S. Pat. No. 6,237,347B1 and JPH02109792A. Also passenger and vehicle transporting vessels with LNG based propulsion have been produced.
LNG is typically stored at a temperature of about minus 162° C. in pressure vessels. Such LNG vessels, or tanks, are larger in size and heavier than diesel oil tanks, e.g. due to the temperature insulation of the tanks. A good utilisation of space is critical in modern vessel design, not least due to economic interests of maximising the space for “payload”, for example space on car decks of RoRo-vessels, or space for cabins, restaurants, etc, in cruise ships. Therefore, positioning of large and heavy LNG fuel tanks poses a problem since they tend to reduce the space available in the vessel.
Also, in view of the hazardous nature of LNG, the positioning of the tanks has to be such that they are protecting, e.g. in that case of a collision or grounding of the vessel.
EP2029421B1 suggests an LNG fuel tank arrangement in a marine vessel, which has a vertically elongated shape, and which is in the vicinity and aligned with a vertical casing for the vessel engine exhaust pipe, (exhaust stack). The fuel tank arrangement comprises a number of tubular tanks which are interconnected with each other. Both the exhaust stack and the fuel tank arrangement are located centrally in the ship, on the ship's centreline.
The vertical tank arrangement may provide some saving of deck space, e.g. on a car deck. Also the location of the vessel's centreline, at a maximal distance from the ship's sides, reduces the risk of tank damage in case of a collision or grounding of the ship.
However, the location of the tank arrangement as suggested in EP2029421B1 will, in particular in passenger ships such as cruise ships, limit possibilities to provide a ship interior that is functional and which facilitates undertakings on the ship, requiring quick movement of crew and easy transport of items, such as luggage, food, equipment, etc.